The present invention relates to a positional sensing transducer which utilizes at least one elongated tube constructed of a magnetically saturable material. One or more sense wires run through each tube parallel to the elongated axis of the tube, and a pair of oppositely poled magnets are positioned on diametrically opposite, exterior portions of the tube so that the magnetic flux from the magnets will completely saturate the portion of the tube that lies between the magnets; while the remaining portion of the tube remains unsaturated.
The use of a ferrite element that is of a toroidal shape and is positioned between two saturating magnets to produce an output signal on a sense line that runs through the core is disclosed in U.S. Pat. No. 3,638,221, issued in the name of Victor M. Bernin on Jan. 25, 1972, and assigned to the assignee of the present invention. The apparatus of the Bernin patent is a keyboard switch in which the entire toroidal core is completely saturated when the magnets are lowered on a keystem into the vicinity of the cores. In order to accomplish the purposes of the Bernin patent, the core of the switch of that patent is positioned so that its axis is parallel to the wide part of the magnets, which are of a substantially greater dimension than is the thickness of the core.
The present invention, by contrast, uses at least one hollow, elongated, cylindrical tube constructed of a material which is magnetically saturable, one or more sense wires that run through the tube and two oppositely polled magnets that move adjacent the outside of the tube in order to provide an accurate linear indication of the position of the magnets with respect to the tube. In other words, the present invention does not provide a binary 1 or 0 output signal; but instead, it may be used to accurately determine the position of the saturating magnets with respect to each tube. The portion of each elongated tube that lies between the magnets is saturated while the remaining portions are not. Because each of the tubes provides a closed flux path, there is no substantial fringing effect at the ends of the saturating magnets; and, therefore, the portion of the tube that is not between the magnets remains substantially unsaturated.
Since the output signal that is provided on the sense wires that run through the tube is primarily dependent upon the position of the magnets with respect to the tube, a very linear output signal is achieved. In addition, problems that generally affect magnetic sensors that depend on partial saturation of the sensing element, such as temperature and aging, are also substantially eliminated. Moreover, the magnetic force that is required to operate the sensing device of the present invention is not critical because of the reliance on complete saturation of the portion of the tube that lies between the magnets to produce an output signal. This is in direct contrast to sensing devices such as those shown in the McAdam U.S. Pat. No. 2,915,637 in which a partial magnetic saturation of the entire toroidal core is employed to provide an output signal.
A prior co-pending United States patent application Ser. No. 518,310, now abandoned, entitled . . . "Positional Transducer Utilizing Magnetic Elements," was filed on . . . Oct. 29, 1974, in the name of Victor M. Bernin and is assigned to the assignee of the present invention. This prior application was directed to a positional transducer that utilized a magnetically saturated, cylindrical, hollow tube in which a single sense wire ran through the passageway in the tube; and the position of a pair of elongated magnets, with respect to the tube, controlled the degree of saturation of the tube so as to provide an output signal indicative of the relative position of the tube and the magnets. The positional transducer of the prior Bernin application was designed so that it could be connected in series with a second separate transducer element of the same type in order to form a sensing circuit, such as an inductive potentiometer or two legs of a two-arm active inductance bridge network.
The present invention is an improvement over the transducer disclosed in the aforementioned Bernin application. In particular, an improved sensing device may be obtained with the present invention since a single unitary magnetic element may be used, thereby substantially eliminating the temperature aging affects that would result if two separate magnetic elements were employed. With the present invention, a two-arm active inductance bridge or four-arm active inductance bridge may be constructed; and the sensitivity of the four-arm active bridge will be approximately two times that of the two-arm active bridge.